B. Field of Invention
The present invention pertains generally to telecommunications and more specifically to time domain multiplexed channels on a single twisted pair.
C. Description of the Background
Telecommunications have grown rapidly over the past few years due to the increasing availability and ease of use of the Internet. Telecommunications companies, particularly local exchange carriers (LECs), i.e., local telephone companies, have experienced growing pains due to the substantial increase in demand for new services. This demand for new services has been created in large part by small customers that obtain data services by attaching to the Internet through analog modems. When a user is attached to the Internet via an analog modem, the local telephone company switch (voice switch) has to allocate a channel for the duration of the call. The analog modem uses tone signals that are generated over a twisted pair that are digitized by the telephone switch at the central office. The use and allocation of voice switches has been based on a model of typical calling patterns for voice calls during peak calling hours before the advent of the Internet. While the average phone call only runs approximately 3 minutes on average, the average Internet connection runs 20 minutes, with the average Internet user being connected to the Internet for 23 hours per month. As more users tie up telephone switches with analog modem data traffic, the number of available channels for voice calls diminishes drastically. This has forced the Telecos to add a great deal of switch capacity in order to meet the required grade of service as defined by the Public Utilities Commission, which is approximately 99.8% availability. Not only have the Telecos been required to outlay significant sums for capital improvement by adding switch capacity, the problem is further exacerbated by the fact that the cost of the new switching equipment is not offset by increased revenue because Internet users are tying up the switches for analog modem data traffic by making local calls which fall under the basic monthly fee for the telephone line. As a result, the profit of Telecos is stagnant or falling with respect to these services.
The voice switch systems used by the local exchange carriers (Telecos or LECs) digitize the tone data emanating from the voice of a speaker, or a modem, to produce a digital signal that can be transmitted through the public switch telephone network (PSTN). These voice switches are designed to maintain a constant connection between the talking parties. This is because it is difficult to carry on a conversation when a voice is not continuous. People perceive subtleties in the nuances of speech. If the voice channel deletes segments of this information, the users have difficulty in carrying on conversations.
Data networks operate in a completely different fashion. A constant open channel is not required to transmit data. Data is bursty by nature and it is relatively insignificant if small delays occur in the transmission of data packets in that the overall data transmission rate is not reduced by packetizing the data transmissions. Data networks are designed to make maximum use of the network by sending data on any available path it can find to a destination and receiving that data in any order and reorganizing it in the proper order. In other words, a portion of a file can be routed through one network path while another portion is routed through a totally different path, with different pieces arriving in an order that is different from the way the data was sent. When the data is received at the other end of the network, the network equipment reassembles the data into the original order. Clearly, voice data cannot be transmitted in this fashion.
The public switch telephone network (PSTN) has used T-1 data services for many years. T-1 is a digital transmission system that was developed to carry digitized voice signals and was later adapted to also carry pure data signals. The T-1 methodology of using clear channels, i.e., dedicated open channels, to carry digitized voice signals is necessary, as indicated above, for carrying these voice signals, but is extremely wasteful of bandwidth when used to carry data. T-1 services were initially offered with full T-1 bandwidth, i.e., 24 channels. As a result, only large corporations could afford the cost of T-1 systems. New services, such as fractional T-1 and frame relay, take advantage of the bursty nature of data to provide lower cost data services over the T-1 infrastructure. These services have brought the cost of T-1 systems down to a level where much smaller companies can afford to link their internal corporate data network with the outside world.
Data networks, such as local area networks (LANs) are typically based on Ethernet, which is a data packet protocol that was designed to transfer data between computers. These networks were not designed to provide voice services as pointed out above. Ethernet has become a de facto corporate network standard because of its low cost and its backwards compatibility with slower predecessors. A need therefore arose to interface these data networks with the PSTN to allow the seamless transmission of data from a local network over the telecommunications system. To meet these needs, bridges and routers were developed that provide the interconnection between the data networks and the PSTN. The bridges and routers perform the data conversions necessary to communicate and transfer data over these incompatible systems.
Although T-1 systems have been modified to provide less expensive services that are affordable for small corporations, a need has existed for even less expensive digital services that are affordable for small businesses and homeowners. ISDN has attempted to fill that need. However, ISDN services have been expensive to implement because these services have required the installation of ISDN digital line cards at the central office (CO) and expensive digital telephones for special terminal adapters at the customer""s premises. As a result, ISDN services have been slow to be deployed in the U.S. In less developed countries where the national telecommunications infrastructure was not fully developed, a significant capital investment was made in ISDN and it has been adopted to a large extent. However, in the U.S., few customers were willing to pay the high cost to change their existing telephone systems for ISDN systems. The cost factor has been exacerbated by the lack of services which the Telecos were providing for ISDN. The high cost factor associated with implementing ISDN, plus the fact that the Internet was not in common use at the time ISDN was first implemented, rendered ISDN a solution to a problem that had not yet been created in the U.S. ISDN is capable of providing 144 Kbps. In the 1970s, 1980s, and early 1990s, this high bandwidth digital service (144 Kbps) was not needed by most customers and their data needs were satisfied by inexpensive standard analog modems which were used to transmit documents via fax. One benefit that has accrued from development of ISDN services is that it has employed 2B1Q coding which is compatible with AMI line coding format that is used in T-1 services. Both of these services can be run in the same wire bundles without causing interference. This is not the case with newer coding formats such as CAP and DMT that are being proposed for the higher speed ADSL systems that run in excess of 8 Mbps.
Due to the lack of widespread adoption of ISDN, the telecommunications industry is leapfrogging this technology to adopt a much faster technology known as Digital Subscriber Line service (DSL). Typical DSL technologies are able to provide data services at data rates ranging from 768 Kbps (HDSL) to rates in excess of 8 Mbps (ADSL, SDSL, and MDSL). The 56 k analog modems (which actually run at 33 Kbps) are woefully inadequate in transferring data at rates required for the graphic intensive presentations that are typically provided on the Internet, or video services such as video on demand, video conferencing, video telephones, and medical imaging, which are technologies that are posed to explode into huge markets once the telecommunications industry is capable of providing the bandwidth needed to deploy these technologies. ISDN services, which are only several times faster than the 56 k analog modems, are now also insufficient for everyone except the most casual Internet user. It is clear that users are requiring sufficiently more bandwidth (faster data transfer rates) than that which can be provided by analog modems or ISDN.
Since DSL lines are not widely available at the current time, corporate demand for more data bandwidth typically comes in the form of additional T-1 lines, while small business and home users can only afford additional analog lines (plain old telephone service or POTS), or in some cases, ISDN service. The demand for additional lines has strained the capacity of the local Telecos (Local Exchange Carriers or LECs) which have attempted to make more effective use of their existing cable facilities by using frequency multiplexed systems in which multiple users are connected to a single twisted pair. However, even these solutions have become strained.
The cost of burying additional cables to run additional POTS lines so that small users can attach to the Internet using analog modems on low cost local calls has become very worrisome to Telecos. The relatively small amount paid for an additional line will not allow the Telecos to recoup their investment for many years and the extended local telephone calls that have resulted from extensive use of the Internet strains the switching capacity of the Telecos, as indicated above. Also, deregulation has allowed for competition in the local loop by Competitive Local Exchange Carriers (CLECs), which also may limit the LECs"" recoupment of their expense in laying additional lines. LECs have attempted to generate some additional profit by acting as an Internet Service Provider (ISP) and charging customers for data services to access the Internet. The fact still remains that a customer can tie up a channel on a LECs"" facility for 24 hours a day, if he or she desires, and only pay the basic monthly fee for the basic POTS service.
Digital Subscriber Line (DSL) technology may provide a solution to many of the problems, as outlined above, of the LECs and may provide more incentive for long distance companies to compete as CLECs. DSL technology can provide both a high speed data service and POTS service on a single line. By deploying DSL to its customers, LECs will be able to charge customers for POTS service, high speed data service and ISP services over a single twisted pair. Since DSL services are capable of providing such high bandwidth, they have a great deal of value in being able to provide graphic intensive Internet presentations, video on demand, video conferencing, etc. as indicated above. As such, DSL services can be priced accordingly. DSL technology uses a Digital Subscriber Line Access Multiplexer (DSLAM) in the central office which separates the voice information from the computer data. The DSL signal comprises an analog voice signal with digital/analog tone data modulated at a much higher frequency on top of the voice data. Frequency filters and de-multiplexers are utilized in the DSLAM to separate these two different frequency modulated channels. The DSLAM routes the voice information to the standard voice switch at the central office and routes the computer information to computer network equipment, such as a router, bridge, switch, etc. In this manner, digital data does not tie up the voice switch and new data services can be provided to the subscriber which are routed around the existing voice switches at the central office. This unloads the voice switches of the LECs from the task of carrying data traffic and eliminates the huge expense of adding switch capacity for analog modem users.
DSL products are available in several different varieties. ADSL, SDSL, and MDSL provide data rates of multiple megabytes per second. SDSL, HDSL, and IDSL provide data rates similar to T-1 rates of 1.544 megabytes per second. All of these different varieties of digital subscriber lines are referred to as xDSLs. The slower DSL technologies have typically used 2B1Q encoding which is capable with T-1 transmissions and does not provide interference when transmitted in the same wire bundle. A typical xDSL implementation utilizes a digital modem that is plugged into the DSL line. The digital modem has a connection for a standard analog phone and an Ethernet port for connection to computer equipment. In this fashion, a single voice line and a computer line are provided to the subscriber over a single twisted pair using typical DSL services.
Although current DSL technology is a solution to many of the problems faced by LECs and provides incentive for others to enter the local telephone market, current DSL technology is limited to broadband digital channel(s) and a single analog POTS channel on a single twisted pair. It would therefore be advantageous to provide a broadband digital channel and multiple analog POTS lines over a single twisted pair in order to provide high bandwidth data services as well as multiple voice services on a single twisted pair. In addition, it would be advantageous to be able to allocate and de-allocate these services in a fashion that is convenient, cost effective, and maximizes the use of the DSL services.
It is against this background, and the limitations and problems associated therewith, that the present invention has been developed.
The present invention overcomes the disadvantages and limitations of the prior art by providing high speed digital DSL services together with multiple voice channels (POTS services) over a single twisted pair. The present invention can dynamically allocate available bandwidth to data services while giving multiple voice channels priority in the dynamic allocation process. In one implementation, the present invention uses time domain multiplexing to provide six 64 Kbps channels on the DSL line. Other implementations may support up to thirty-two 64 Kbps channels. These channels can be dynamically allocated (on the fly) between POTS services and data services. As implemented, the POTS circuits always take precedence over the data circuits. If no POTS circuits are active, then all channels are allocated to the data services, providing a maximum throughput of 384 Kbps to 2.048 Mbps. When an incoming call is received, the present invention will de-allocate a 64 Kbps channel from the data bandwidth and reserve that channel as a clear channel for voice data. This channel will remain dedicated to the voice call as long as the call is in progress. When the call has been completed, the 64 Kbps channel is automatically reallocated to data services. If all channels are allocated to POTS services, there could be no data services available until a POTS circuit is released. The present invention also uses automatic de-allocation of data channels after packet transmission. In other words, data packets are transmitted over channels that are available to data services. Once a packet is transmitted, that channel is automatically de-allocated and made available for use as either a POTS line or transmission of additional data packets. Data packets can be distributed over all of the available channels for both transmission and reception. Automatic de-allocation, as soon as the transmission is completed, allows for maximum use of the available data services.
The present invention may therefore comprise a method of providing a predetermined number of multiple channels on a single digital subscriber line for the transmission of voice signals and data signals and maximizing the number of channels available for transmission of the data signals to maximize the data transmission rate of the data signals while making all channels available for transmission of the voice signals comprising the steps of: time division multiplexing the digital subscriber line to provide the predetermined number of multiple channels on the digital subscriber line; allocating clear channels from the predetermined number of multiple channels for the voice signals that are initiated over the digital subscriber line; de-allocating the clear channels upon termination of each of the voice signals; transmitting the data signals over open channels, that are not allocated as clear channels for transmission of the voice signals, such that the data signals are distributed across the open channels to provide a high data transmission rate.
The present invention may further comprise a method of transmitting multiple voice signals between a central office switch located at a central office and multiple POTS lines connected to a remote terminal, and transmitting data signals between a central office data port located at the central office and a subscriber data port connected to the remote terminal comprising the steps of: providing a digital subscriber line between the central office and the remote terminal, the digital subscriber line having multiple time domain multiplexed channels for carrying both the multiple voiced signals and the data signals; directing the data signals received from the digital subscriber line at the central office to a central office data port; directing the multiple voice signals received from the digital subscriber line at the central office to the central office switch for distribution to the public switched telephone network; directing the data signals received by the remote terminal from the digital subscriber line to the subscriber data port; directing the multiple voice signals received by the remote terminal from the digital subscriber line to the multiple POTS lines; allocating the multiple time domain multiplexed channels so that all of the multiple time domain multiplexed channels are available for the transmission of the multiple voice signals and all remaining open channels are available for transmission of the data signals.
The present invention may further comprise a system for transmitting multiple voice signals and data signals over a multiple channel digital subscriber line comprising: a remote terminal connected to the digital subscriber line that directs data signals between the multiple channel digital subscriber line and a data port and directs voice signals between the multiple channel digital subscriber line and multiple POTS lines; a central office terminal controller connected to the multiple channel digital subscriber line that directs data signals between the multiple channel digital subscriber line and a central office data port, and directs voice signals between the multiple channel digital subscriber line and a central office switch.
The advantages of the present invention are that multiple POTS lines can be provided as well as data services over a single twisted pair using high speed DSL services. This is accomplished by dynamic allocation of multiple TDM channels with POTS services taking precedent over data services. The manner in which this invention is implemented allows POTS circuits up to 23,000 feet from the central office or from a fiber node. Additionally, the number of channels that are made available to a subscriber can be simply programmed from the central office without the need for additional hardware. The present invention can be configured and controlled using the operations and support system in the central office of the LEC or via standard SNMP software using TCP/IP protocol, or with a standard browser program such as Netscape or Microsoft Explorer. Ease of use and familiarity of such software systems by central office employees facilitates the implementation of the present invention. Another advantage of the present invention is that it uses standard 2B1Q line coding which maintains a compatibility with existing services, such as T-1, in cable bundles. Additionally, the present invention is easy to install as a standard network interface unit. The provisioning of lines, or channels, in accordance with the present invention is a process that is known and understood by service personnel. Further, field personnel do not have to be concerned with reconfiguring the system since it is fully configurable from the central office. Also, the grade of service provided to the customer can be changed at any time to the network management system at the central office without the need of special services. Additionally, the present invention can be implemented with line cards that can be easily replaced to upgrade the system as faster data services become available.